A virtual image display apparatus (an image display apparatus) for presenting a two-dimensional image formed by an image generating device as an enlarged virtual image to a viewer through a virtual image optical system is known from JP 2006-162767 A, for example.
As shown in a conceptual diagram in FIG. 21, this image display apparatus 1100 includes: an image generating device 111 having a plurality of pixels arranged in a two-dimensional matrix; a collimator optical system 112 that converts light emitted from the pixels of the image generating device 111 into a parallel light beam; and a light guiding unit 120 that guides and emits the incident light converted into the parallel light beam by the collimator optical system 112. The light emitted from the light guiding unit 120 is guided to an eye 21 of a viewer 20. The light guiding unit 120 includes: a light guide panel 121 that propagates incident light therein by total reflection, and then emits the light; a first deflecting unit 130 (formed with a single light reflecting film, for example) that reflects the light that has entered the light guide panel 121 so that the light that has entered the light guide panel 121 is totally reflected inside the light guide panel 121; and a second deflecting unit 140 (formed with a multi-layer light reflecting film having a multi-layer stack structure, for example) that emits the light propagated inside the light guide panel 121 by total reflection from the light guide panel 121. Then, when such an image display apparatus 1100 constitutes, for example, an HMD, a reduction in the weight and the size of the device can be realized.
Alternatively, a virtual image display apparatus (an image display apparatus) that uses a hologram diffraction grating to present a two-dimensional image formed by an image generating device as an enlarged virtual image to a viewer through a virtual image optical system is also known from JP 2007-094175 A, for example.
As shown in a conceptual diagram in FIG. 22, this image display apparatus 1200 basically includes an image generating device 111 that displays an image, a collimator optical system 112, and a light guiding unit 220 that receives light from the image generating device 111 and guides the light to an eye 21 of a viewer. Here, the light guiding unit 220 includes a light guide panel 221, and a first diffraction grating member 230 and a second diffraction grating member 240 that are formed with a reflective volume hologram diffraction grating provided on the light guide panel 221. Then, a parallel light beam emitted from the collimator optical system 112 enters a first surface 222 of the light guide panel 221, and is emitted from the first surface 222. The first diffraction grating member 230 and the second diffraction grating member 240 are attached to a second surface 223 of the light guide panel 221 that is parallel to the first surface 222 of the light guide panel 221.